<style type="text/css">
#da {
	position:absolute;
	width:400px;
	height:300px;
	left:0;
	top:0;
	background:#c00;
	z-index:1;
}
#db {
	width:400px;
	height:300px;
	position:absolute;
	left:100px;
	top:100px;
	background:#00c;
	z-index:2;
}
.dz {
	z-index:10;
}
</style>
<div id = 'da'>
	<div style="z-index:10;background:#f00;height:250px;">Z-index:10.background:#f00</div>
</div>
<div id='db'>
	<div style="z-index:1;background:#00f;height:250px;">Z-index:1,background:#00f;</div>
</div>